The broad goals of this project are to understand the control of enzyme formation in biosynthetic pathways, particularly of those in arginine synthesis and methionine synthesis in Escherichia coli. Recently a cell-free system has been developed for the synthesis of two of the arginine enzymes, acetylornithinase and argininosuccinase. As a source of DNA, transducing phages carrying the structural genes (E,H) for these enzymes have been obtained. In the future, details of the biochemical mechanism of repression are to be studied in these systems and in systems involving two enzymes of methionine synthesis, the non-B12 transmethylase (metE) and folate reductase (metF). Such details include isolation and characterization of the repressors, binding of the repressor to operator sites for various structural genes, determination of the nature of he corepressors and test for repression at the levels of transcription and translation. A phage carrying the structural gene for the feedback enzyme of the arginine pathway has been isolated and will be used in an effort to obtain and characterize this enzyme in cell-free extracts. Also, arg-lac z fusions on phage lambda have been isolated for genes argA, argG and argE. This will facilitate greatly the study of regulation of enzyme synthesis in vitro.